Fuse construction



May 8, 1951 H. v. DRYER FUSE CONSTRUCTION Filed April 28, 1948 i 30 Z/lafff/rg- 0^/ A5/5 of 707,44 AAPC 5A/6TH 7. 6. 5. 4. 5. 2. QQQQQQQR lwww Patented May 8, 1951 FUSE CONSTRUCTION Henry V. Dryer, 'MilwaukeaWis., assigner to .McGraw Electric Company, a corporation of DelawareApplication Aprl`28, 1948, .Seria.l.No. 23,711

-Claims.

This invention relates toa fuse .construction and is particularlydirected'to a current limiting cartridge type of fuse construction.Current limiting cartridge type fuses have frequentlybeen filled withsand or other granular material -to provide an extensivecondensing-andrcocling surface, but these constructions Ahave :notalways proven satisfactory. For example, Iin certain types of sand lledfuses it has been found that a fulgurite is Vfrequently formed undercertain conditions which is conducting at very-high-temperatures andconsequently interferes with the desired or correct action of the fuse.Also, certain types ci sand-filled fuses create an .excessively highvoltage surge onthe -line When'the fuse Wire ruptures, which in someycases has caused breakdown or flashover of ynearby insulation.

Objects of this invention are to provide aifuse construction in whichsand or other granular refractory material is provided-at yopposite endsof the cartridge type Vfuse vto provide expansion zones for the gasesgenerated by the blowingoi the fuse linie and to provide-extended-surfaces Which act as cooling and'condensing surfaces for the hotgases, and to provide intermediate the portions ci sand a materialwhich, when acted upon by the arc, evolves a water vapor orother vaporwhich chills the arc and also quickly cools any fulgurite that may beformed in thesand and prevents it from reaching a temperature so highthat it would'becomea conductor.

Further objects of this invention Vare to providea very simple type ofconstruction Vin'which, though lthe vdevice is a closed cartridge typeof fuse, nevertheless the pressure generated on blo-W- ing of the fuseeven on heavy short-circuit 'currents never reaches an excessive or2dangerous value.

A still further object of this invention .is to provide a currentlimiting vtype of fuse which does notdevelop an excessive `voltage surgewhen the fuse blows.

An embodiment Vof the invention is vshow-n Lin the accompanyingdrawings, .in which:

Figure l is a longitudinal, sectional view through the cartridgetypefuse.

Figure 2 is a chart showing the effecto'fdifferent per cents of bauxiteupon the ratio Vof the actual maximum current, .whenrupture occurs, tothe maximum availablecurrent.

Figure 3 is a chart showing curvesillustrating the eii'ectiveness .ofvlthe bauxite and :sand .-ar rangement in reducing Ivthe arclength-equivalent to length ci fuse Wire-required Lto rclear :in :an

2 ordinary sand-lilled fuse when both Vare operating under the samecircuit conditions.

Any suitable type of cartridge type fuse can be employed. For instance,the cartridge fuse may be of the type disclosed in my ccpendingapplication Serial No. 11,132, led February 26, i948, for FuseConstructions, which has issued as Patent No. 2,490,950, dated 'December13, 1949. This cartridge type of fuse is illustrated in 'Figure l andmay comprise a Bakelite or'other outer tubular casing I provided with aclear acrylic transparent plug 2 screwed therein and with end conductingcaps 3 and 5. VIt is understood that the indicator shown in Figure l isnot essential to the proper operation of the fuse in clearing thecircuit. The end conducting caps are in electrical connection with endiittings 5 and E between which a ribbed, ceramic supporting rod .'I isheld. This ceramic supporting rod may be notched as indicated at 8 toposition a portion of the fuse link 9 wrapped therearound immediatelyadjacent the inner end of the transparent plug. This construction, ofcourse, can be varied as will be lseen as the description proceeds, butis merely detailed as one of the possible forms that the invention maytake. .Sections of sand I!! and Ii are located adjacent opposite ends oftheiinterior Vof the tubular casing I and 'a section of .bauxite I2 islocated approximately centrally betweenthe two sand sections IB and II.Many othergranular or vgranulated refractory materials, as for examplequartz, silica, alumina, or magnesia may be .used in place of the sand.A quartz or silica sand and bauxite are the most practical comb-inationof materials from the standpoint of `eiliciency of operation as Well as10W cost. The ends of the fuse link 9 are attached in any suitablemannennot shown, to the ttings 5 and 6. Gbviously, other types of fuseconstructions could be employed'. For example, with lower voltage fuselinks it would not be necessary to use the ceramic supporting rod '1,but on high voltage fuse links of small diameter it is found moreconvenient to support the fuse link Von the ceramic rod 1. However, thisinvention is primarily concerned with the arrangement cf the bauxite andthe sand, granular quartz, or other granular refractory material.

It has been Vfound that when the fuse link blows, thatit almostinvariably ruptures initially in the region which is surrounded bybauxite. On very `high currents the initial rupture point vis notdiscernible since the fuse Wire melts almost instantaneously along itsentire length. The sandsections AIl) and yI I provide expansion area-Stures.

and prevents it from reaching a temperature so high that it would becomea conductor and thus support the arc and thus .causejfailure of thedevice.

Figure 2 shows the effect of variations in the per cent of bauxite onthe current limiting ability of the fuse. The abscissa indicate the percent of bauxite on the basis of the'per cent of the total arc length,that is to say, on length of arc in the bauxite area in Figure 1 to thetotal arc length between the fittings 5 and The ordinates represent theratio of the actual value to which the current is limited by the fusewhen rupture occurs to the maximum available current. The curve istypical of a fuse embodying the arrangement of materials shown in Figurel.

It will be seen that the greatest current limitation is obtained whenapproximately thirty per cent o1' less of bauxite is used.

It is possible to construct either an all-sand or an all-bauxitecartridge type of fuse that will operate satisfactorily under certainconditions. However, either material when used alone imposes certainlimitations or undesirable fea- For example, an all-sand fuse createsvery little internal pressure and is very effective in limiting thefault current, but frequently causesl an excessively high voltage surgeat the time of rupture. On the other hand, an allbauxite fuse results ina relatively low and inconsequential voltage surge but is not aseffective in limiting the fault current and at high currents producesrather high internal pressures at the time of rupture.

Thus by using a construction embodying the arrangement illustrated byFigure l, the designer, by varying the percentage of the materialsinvolved, may construct a fuse having nearly any combination and degreeof the above characteristics desired. For example, a fuse constructionof this type containing approximately twenty per cent of bauxite is apractical compromise combining the most desirable features for generaluse in the industry.

Figure 3 shows a chart in which curves A and B show a typicalrelationship between the minimum arc length required to clear and thesystem voltage for sand as indicated by the curve A and for sand plustwenty per cent bauxite as indicated by the curve B. It will .be seenthat the combination of sand with twenty per cent bauxite will clear insubstantially half the minimum length as that required for sand alone.

It will also be seen from reference to Figure 2, that the fuseconstruction limits the short-circuit current to a value well belowthemaximum available current, particularly so where twentyfive to thirtyper cent or less of bauxite is used.

The bauxite remains non-conducting even at high temperatures and servesthe highly useful purpose of evolving a quantity of chilling water vaporas previously described. Preferably, the bauxite is a ne powderedmaterial and the sand is a clean, ne grained quartz or silica sand.

It has been found that cartridge type fuses constructed in accordancewith this invention do not allow the internal pressure to rise to adangerous point even when blown under heavir short-circuit conditions.It has been found also that these cartridge type fuses, Whetherconstructed in the exact form shown in Figure l or in some other form,can be very cheaply manufactured provided the bauxite and sand areassociated and used in the manner indicated. AThese relatively cheapcartridge type fuses are intended to be discarded after blowing and tobe Areplaced with new cartridge type assemblies.

Although this invention has been described in considerable detail, it isto be understood that such description is intended as illustrativerather than limiting, as the invention may be variously i embodied andis to be interpreted as claimed.

I claim:

l. A fuse construction comprising a tubular outer casing, terminalsadjacent opposite ends thereof, a fuse link extending through saidcasing and electrically connecting said terminals, bauxite within saidcasing adjacent an intermediate portion of said fuse link, and sandwithin said casing on opposite sides of said bauxite.

2. A fuse construction comprising a tubular outer casing havingterminals adjacent opposite ends, a fuse link within said casingelectrically connecting said terminals, bauxite within said casing andgranular refractory material within said casing, said bauxite andgranular refractory material being in contact with said fuse link andsaid granular refractory material arranged to provide extensive coolingand condensing surfaces for the gases and vapors incident to rupture ofsaid fuse link.

3. A fuse construction comprising a tubular outer casing, terminalsadjacent opposite ends thereof, a fuse link extending through saidcasing and electrically connecting said terminals, bauxite within saidcasing adjacent an intermediate portion of said fuse link, and sandWithin said casing on opposite sides of said bauxite, said bauxite beingnot more than approximately thirty per cent of the total length of saidsand and bauxite as measured along the active length of said fuse link.

4. A fuse construction comprising a tubular outer casing, terminalsadjacent opposite ends thereof, a fuse link electrically connecting saidterminals and extending through said casing, a cooling agent includingbauxite located Within said casing adjacent an intermediate portion ofsaid fuse link, and a granular refractory substance within said casingand located on opposite sides of said bauxite and arranged to provideextensive cooling and condensing surfaces for the gases and vaporsincident to rupture of said fuse link.

5. A fuse construction comprising a tubular outer casing havingterminals adjacent opposite ends, a fuse link within said casingelectrically connecting said terminals, bauxite within said casing andsand within said casing, said bauxite and sand being in contact withsaid fuse link and said sand arranged to provide extensive cooling andcondensing surfaces for the gases and vapors incident to rupture of saidfuse link.

6. A fuse construction comprising a tubular outer casing havingterminals adjacent opposite ends, a fuse link within said casingelectrically connecting said terminals, powdered bauxite within lsaidcasing and granular refractory material withinsaid casing, said powderedbauxite 5 and granular refractory material being in contact with saidfuse link and said granular refractory material arranged to provideextensive cooling and condensing surfaces for the gases and vaporsincident to rupture of said fuse link.

HENRY V. DRYER.

REFERENCES CITED NTED STATES PATENTS Number 1 The following referencesare of record in the 10 Number le of this patent:

Name Date Schattner Feb. 1, 1910 Banks May 26, 1914 Cole May 25, 1915McMahon Aug. 26, 1941 Schuck Aug. 25, 1942 FOREIGN PATENTS Country DateGreat Britain Jan. 22, 1936

